A smart grid is a concept to solve a problem of power transmission between a supplier and a consumer actively using information technology, and has a purpose of constructing an intelligent transmission network without wasting energy and with minimal costs.
As a specific system using the smart grid, for example, a smart meter has been suggested. The smart meter is a system including a high functionality electric meter with a communication function and a function of managing other appliances. When the smart meter system is used, communication or control can be performed through an electric meter which is installed as a part of the equipment of a power consumer. For example, the smart system can notify the measurement result of power consumption amount spent by the power consumer to a power supplier using a communication function built into the electric meter. For this reason, the power supplier may omit the operation of reading the electric meter for charging the electricity usage rates.
On the other hand, when the power supplier provides solar cell equipment or wind power generation equipment as power generation equipment, for example, the electric generation capacity is not constant and is changed moment by moment as environmental conditions such as weather, wind force and wind direction change. For example, even when the power consumption amount is constant, in a case where the power generation capacity is insufficient due to a decrease in the power generation capacity, it is necessary to use thermal power generation or other power generation equipment to make up for the insufficient power and power generation costs may change remarkably according to fuel consumption.
As an application of the smart grid, a variable rate system of electricity rates (real time pricing) has been under review. In other words, the electricity rates per unit power consumption amount of each consumer are changed to the optimal rates based on the relation between the power generation capacity and power consumption amount. The electricity rates are changed such that when the power consumption amount is relatively high, the electricity rates are high, and when the power consumption amount is relatively low, the electricity rates are low. In this case, the power supplier can ascertain the power consumption amount of the consumer in each place using the smart meter, determines the electricity rates per unit power consumption amount as the optimal rates sequentially based on the relation between the power generation capacity and the power consumption amount, and notifies the latest electricity rates to the consumer of each location using the smart meter in real time.
As the related art of the invention, for example, the technologies which are disclosed in PTL 1, PTL 2, PTL 3, and PTL 4 are known.
In PTL 1, it is suggested that timer means be provided to identify a time slot division to which the present time belongs to display a unit price of electricity rates predetermined in every time slot on an indoor display device.
In PTL 2, it is suggested that a power strip have a power consumption measurement function and calculate the electricity rates per hour and the accumulated electricity rates based on the measured power consumption and the unit price of electricity rates to display the result. The unit price of the electricity rates used in the calculation can be changed and a warning display may be shown when the power consumption is more than a predetermined value.
In PTL 3, it is suggested that an air conditioner have a function of measuring power consumption, calculate electricity rates for a predetermined period (a day's worth) during operation based on the measured power consumption, and warn a user of the electricity rates by flashing a display unit when the electricity rates become close to a predetermined value.
In PTL 4, technology is suggested that an electricity meter to which various electrical appliances are connected have a special algorithm process function which analyzes a detected voltage or current consumption and separate power consumption amount of each electrical appliance from the total power consumption amount to display the power consumption amount.